The early stages of rnetal/polymer interface formation between aluminum and poly(2,5,2',5'-tetrahexyloxy-8,7'-dicyanodi-~-phenylenevinylene) or their ring-substituted derivatives have been studied theoretically by using quantum-chemical calculations as well as experimentally by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. This class of conjugated polymer is of interest in the development of organic light-emitting diodes. The theoretical and experimental results indicate that aluminum preferentially reacts with the polymer by forming covalent bonds with the nitrogen and carbon atoms of the cyano groups. When the side chains of the phenylene rings include carbonyl groups, however, the theoretical results indicate that the carbonyl moiety is another preferred site of interaction. Keywords light-emitting diodes ' Polymers Semiempirical calculationselectroluminescence ' PolYmer/metal interface ' 1 field-effect trans is tors,"'^ 141 or nonlinear optical materials.[', "1
Light-emitting diodes in which thin films of conjugated polymers constitute the active layer were first reported in 1990 by Friend and co-workers, who succeeded in fabricating an LED with poly(p-phenylene vinylene) (PPV) as the emission layer, IT0 as the hole-injecting electrode. and aluminum as the electron injecting electrode. ['] Interest in this field then grew rapidly, [